Documentation: dmaengine: document DMA_CTRL_ACK
Add documentation about acking the transfers, and their reusability. Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr> Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com> Signed-off-by: Vinod Koul <vinod.koul@intel.com>
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@ -345,11 +345,12 @@ where to put them)
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that abstracts it away.
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* DMA_CTRL_ACK
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- Undocumented feature
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- No one really has an idea of what it's about, besides being
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related to reusing the DMA transaction descriptors or having
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additional transactions added to it in the async-tx API
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- Useless in the case of the slave API
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- If set, the transfer can be reused after being completed.
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- There is a guarantee the transfer won't be freed until it is acked
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by async_tx_ack().
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- As a consequence, if a device driver wants to skip the dma_map_sg() and
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dma_unmap_sg() in between 2 transfers, because the DMA'd data wasn't used,
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it can resubmit the transfer right after its completion.
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General Design Notes
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--------------------
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